Add doctests of Connection + Cache behavior.

src/ZODB/tests/test_cache.py

+##############################################################################
+#
+# Copyright (c) 2004 Zope Corporation and Contributors.
+# All Rights Reserved.
+#
+# This software is subject to the provisions of the Zope Public License,
+# Version 2.0 (ZPL).  A copy of the ZPL should accompany this distribution.
+# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
+# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
+# FOR A PARTICULAR PURPOSE.
+#
+##############################################################################
+"""Test behavior of Connection plus cPickleCache.
+
+Methods involved:
+get()
+add()
+cacheFullSweep()
+cacheMinimize()
+invalidate()
+
+Other:
+resetCache()
+
+cache internal issues:
+cache gets full
+when incrgc is called
+gc
+
+Need to cover various transaction boundaries:
+commit
+abort
+sub-transaction commit / abort
+-- can provide our own txn implementation
+"""
+
+import doctest
+import unittest
+
+from persistent import Persistent
+from ZODB.config import databaseFromString
+
+class RecalcitrantObject(Persistent):
+    """A Persistent object that will not become a ghost."""
+
+    deactivations = 0
+
+    def _p_deactivate(self):
+        self.__class__.deactivations += 1
+
+class CacheTests(unittest.TestCase):
+
+    def test_cache(self):
+        pass
+
+    def test_cache_gc_recalcitrant(self):
+        r"""Test that a cacheGC() call will return.
+
+        It's possible for a particular object to ignore the
+        _p_deactivate() call.  We want to check several things in this
+        case.  The cache should called the real _p_deactivate() method
+        not the one provided by Persistent.  The cacheGC() call should
+        also return when it's looked at each item, regardless of whether
+        it became a ghost.
+
+        >>> db = databaseFromString("<zodb>\n"
+        ...                         "cache-size 4\n"
+        ...                         "<mappingstorage/>\n"
+        ...                         "</zodb>")
+        >>> cn = db.open()
+        >>> r = cn.root()
+        >>> L = []
+        >>> for i in range(5):
+        ...     o = RecalcitrantObject()
+        ...     L.append(o)
+        ...     r[i] = o
+        >>> get_transaction().commit()
+        >>> [o._p_state for o in L]
+        [0, 0, 0, 0, 0]
+
+        The Connection calls cacheGC() after it commits a transaction.
+        Since the cache will now have more objects that it's target size,
+        it will call _p_deactivate() on each RecalcitrantObject.
+        
+        >>> RecalcitrantObject.deactivations
+        5
+        >>> [o._p_state for o in L]
+        [0, 0, 0, 0, 0]
+
+        An explicit call to cacheGC() has the same effect.
+
+        >>> cn.cacheGC()
+        >>> RecalcitrantObject.deactivations
+        10
+        >>> [o._p_state for o in L]
+        [0, 0, 0, 0, 0]
+        """
+
+def test_suite():
+    return doctest.DocTestSuite()